Production of hydrogen



Sept. 21, 1948. F. T. BARR 2,449,635

PRODUCTION OF HYDROGEN Filed Oct. 9.194s

SPEN T REDUCING 64$ STAMP/PE z UPFLOW STHADPIPE STWVD PIPE REA C a flank713m",

ALTE'RMTE Patented Sept. 21, 1948 PRODUCTION OF HYDROGEN Frank T. Barr,Summit, N. J assignor, by mesne assignments, to Standard CatalyticCompany, a corporation oi Delaware Application October 9, 1946, SerialNo. 702,301 In Canada March 19, 1943 3 Claims. 1

The present invention relates to the production of hydrogen, inparticular, to high pressure hydrogen for synthesis processes. Theinvention will be fully understood from the following description andthe drawing.

This application contains subject matter which was, in part, disclosedand claimed in my abandoned application Serial No. 432,563, filedFebruary 27, 1942.

Heretofore hydrogen has been produced by'reaction of metals such as ironand superheated steam in which reaction the steam is reduced by themetal at elevated temperature with the simultaneous formation of a metaloxide. In a subsequent step the metal oxide is reduced, for example bywater gas, and can be reused for further hydrogen production.

Such processes have heretofore been operated intermittently using acyclic system of fixed bed reactors alternating between hydrogenproducing and metal reducing stages. Systems of this type suffer greatlyfrom various inherent economical and technical disadvantages.

For instance, product quality and yields suffer from the ineiflciency ofthe cyclic purging procedure required and change during the process ofeach producing cycle because of the change in temperature and/orpressure with time. The rate of conversion is low requiring extremelyhigh temperatures as a result of the small surface of the metal whichmust be used in the form of relatively large lumps to avoid excessivepressure drop across the metal bed. These high temperatures weaken thephysical structure of the metal lumps by sintering, spalling or the likewhich causes plugging and channelling.

When high pressure hydrogen is to be produced not only the reactingsteam supplied during the production stage but also the reducing gasesused in the reduction stage must be compressed to high pressures unlessdepressuring and repressuring in each cycle is undertaken, a step whichis time consuming, complicates operation and reduces capacity. The costof compressing the extremely large quantities of reducing gas requiredis close to prohibitive commercially and no appreciable savings areobtained by alternate depressuring and repressuring the reactors for thereducing and producing cycles. For these reasons the conventionalmetal-steam process has failed to assume commercial importance for theproduction of hydrogen at high pressures as is desirable for varioussyntheses, for example highpressure hydrogenation of carbonaceous mate 2rials, hydrocarbon synthesis from C0 and H2 in the presence of iron-typecatalysts, etc. 7

The present invention overcomes the aforementioned difiiculties andaffords various additional advantages as will be fully understood fromthe following detailed description.

It is, therefore, the principal object of the present invention toprovide an improved method of producing hydrogen by the reduction ofsteam.

Another object of my invention is to provide an improved continuousprocess for the production of \hydrogen by the reduction of steamwithout the disadvantages of fixed bed intermittent operation.

A more specific object of the present invention is to provide animproved continuous process for the production of high pressure hydrogenby the reduction of steam with metalliferous reducing agents wherein thereducing agent is oxidized and regenerated by reduction and wherein theregeneration of the reducing agent may be carried out at a lowerpressure than the steam reduction without affecting the economies of theprocess.

Other objects and advantages will become apparent from the followingdisclosure and claims.

In accordance with the present invention, the steam to be reduced tohydrogen iscontacted in a hydrogen generation zone at reducingconditions of temperature and pressure with a dense turbulent ebullientmass of a finely divided solid metalliferous reducing agent such as areduced metal oxide fluidized by the upwardly flowing gaseous reagentsand reaction products to form a well defined upper level. The spentsolid reducing agent, largely consisting of metal oxide, is

continuously passed under the pseudo -hydrostatic pressure of afluidized column of spent reducing agent to a regeneration zone whereinit is regenerated with a fluid reducing agent at reducing conditions oftemperature and pressure in the form of a dense turbulent ebullient massof finely divided solids fluidized byan upwardly flowing gas to form awell defined upper level. Finely divided regenerated metalliferousreducing agent is continuously returned to the hydrogen generation zoneunder the pseudo-hydrostatic pressure of a fluidized column ofregenerated reducing agent.

In accordance with a preferred embodiment of my invention, the hydrogengeneration zone is operated at a pressure substantially higher than thatof the regeneration zone and the latter is located sufficiently highabove the hydrogen generation zone to permit the maintenance of a'action to either reaction zone.

fluidized solids column between the two zones, which exerts on its basea pseudo-hydrostatic pressure at least'equal to the pressure of thehydrogen generation zone. This column may be used to pass regeneratedsolid reducing agent continuously from the low pressure regenerationzone to the high pressure hydrogen generation zone without affecting theuniformity of the reaction conditions and the continuity of operation ineither zone.

It will be appreciated from the foregoing that my process may beoperated continuously at optimum conditions. The increased surface ofthe finely divided metalliferous reducing agent permits the use of lowerreaction temperatures and results in a greater percentage conversion ofsteam into hydrogen at conditions under which no danger of sintering,plugging or channelling exists.

Both the hydrogen generation and the regeneration reactions areendothermic or only slightly exothermic so that heat must be supplied tothe system. This may be accomplished by preheating the solid and fluidreactants to suitable temperatures and supplying additional heat of re-However, the necessary heat may be supplied in the most enicient mannerby conducting thehydrogen generation at a substantially lowertemperature than the regeneration and supplying at least a substantialportion of the heat required for the hydrogen generation in the form ofa sensible heat of solids circulated from the regeneration zone to thehydrogen generation zone. Hydrogen generation temperatures of about800-1500 F., preferably 9501350 F., and regeneration temperatures ofabout 800-1700 R, preferably 1200-1500'F., are generally suitable forthis purpose when the system FeOdFeaOr is used. While it is generallypreferable that regeneration be carried out at a temperature higher thanhydrogen generation, operation with generation temperature higher thanregeneration temperature may be employed if desired.

While the heat supply to the regeneration zone may be accomplished byapplying equipment for the indirect supply of heat from an outside heatsource, I prefer to generate heat within the regeneration zone byintroducing fuel and an oxidizing gas together with the reducingmaterial and conducting a limited combustion within the regenerationzone under overall reducing conditions.

A great variety of materials may be used as fuel and reducing material.When methane or similar hydrocarbon gases are used as fuel and/orreducing agent, temperatures in the neighborhood of 1400-1500 F. shouldbe employed, lower temperatures tending to promote the formation ofhydrogen instead of reduced metal oxide and substantially highertemperatures lying in the range wherein reduced metal oxides such asiron or low oxides of iron tend to sinter and agglomerate. Mixtures ofCO and H2 such as watergas may also be used and usually at somewhatlower temperatures due to the large proportion of carbon present.

A particular advantage of my invention resides in the fact that evensolid carbonaceous materials such as finely divided coal or coke may becharged to the' regeneration zone as fuel and/or reducing agent,affordin even higher proportions of carbon to hydrogen and permittingthe use of still lower regeneration temperatures. In conventional fixedbed cyclic operation,the difllculties generate the desired amount ofheat.

of solids distribution and temperature control are such as will causethe retention of appreciable amounts of carbon on the regeneratedmetallic agent when carbonaceous regenerating agents are used. Thisgives rise to the formation of carbon oxides in the hydrogen generationzone and to a consequent contamination of product hydrogen. The idealconditions of materialsand heat-distribution in a fluidized solids'massof the type employed in accordance with my invention assure completeconsumption of the total carbon present in the regeneration zone.

The amount of air and/or oxygen supplied to the regeneration zone forcombustion depends on the amount of fuel required to be burned to Ingeneral, about 0.1 to 1.0 lbs. of carbonaceous fuel and 0.15 to 2.5 lbs.of oxygen per lb. of carbonaceous reducing agent are sufficient tomaintain the heat balance of the process When the metallic materialcirculated between the hydrogen generation and metal regeneration zonesessentially comprises FeO and F6304 and superheated steam of about 400to 1100 F. and atmospheric to 300 lbs. pressure is supplied to thehydrogen generation zone.

The amount of heat-carrying solids circulated from the regeneration zoneto the hydrogen generation zone should be sufiicient to bring the inlettemperature ,of the latter zone at least to the desired reactiontemperature. Reactor temperatures of about 950-1350 F. may beestablished by circulating about 0.5-1.5 lbs. of iron in the form of FeOhaving a temperature of about 1200- 1500 F. or about 0.1-0.8 lbs. ofiron in the form of Fe of the same temperature per standard cu. ft. ofhydrogen to be produced. Solids circulation rates in the oppositedirection should be subof such impure or relatively undesirable hydrogenallows practically complete utilization of the hydrogen in the reducingstep, by recycling offgases from the regenerator back to the regeneratorafter removal of water vapor by simple condensation.

The conditions of solids particle size, linear gas velocities, anddensities of fluidized solids columns and reactor beds may be thosegenerally employed in fluid solids operations. More specifically, solidsparticle sizes of about 20-400 mesh, preferably -200 mesh, linear gasvelocities of about 0.1-5 ft., preferably 0.3-1 ft. per second and beddensities of about 10-150 lbs., preferably 15-75 lbs. per cu. ft. may beemployed.

The height of the fluidized solids columns used to circulate the solidsdepends on the pressure differential between the hydrogen generation andmetal regeneration zones. The hydrogen generation zone may be operatedat pressures varying from atmospheric to 100 atmospheres or higher,pressures of about 5-20 atmospheres being preferred for the productionof high pressure hydrogen used in the hydrocarbon synthesis over ironcatalysts. For this purpose, a fluidized solids column having a heightof about 50 to 200 it. at a density of from about 50 to about 250 lbs.per cu. it. may serve to circulate solids from an elevated regenerationzone to the hydrogen generation zone. The return circulation may takeplace in the form of a relatively dilute suspension under the pressureof the hydrogen generation or with the aid of a so-called reversestandpipe as will appear more clearly hereinafter.

The metalliferous material used for the steam reduction may be metalliciron which is oxidized to FeO, or preferably FeO which is oxidized toF6304. Alloys of iron such as ferro-manganese, ferro-chrome, compositesof copper oxides and iron, as well as tin oxides, various manganeseoxides, or the like may also be used.

Having set forth its general nature and objects, my invention will bebest understood from the following more detailed description whereinreference will be made to the accompanying drawing which is asemi-diagrammatic view of apparatus adapted to carry out a preferredembodiment of the invention.

Referring now to the drawing, the system illustrated therein essentiallycomprises a hydrogengenerating reactor l and a metal regenerator 30, thefunctions and cooperation of which will presently be described.superheated steam under a pressure of about 50-150 lbs. per sq. in., sayabout 105 lbs. per sq. in. is supplied to line I wherein it is mixedwith reduced metallic material say substantially FeO having an averageparticle size of about 200 mesh supplied from, and substantially at thetemperature of, regenerator 30 through standpipe 40 as will appear moreclearly hereinafter. A suspension of finely divided FeO in steam, havinga temperature of about 1200 F., passes under the pressure of the steamand the pseudo-hydrostatic pressure of the fluidized solids column instandpipe 40 to the lower conical portion of reactor III which it entersthrough a distributing grid 5.

The linear velocity of the steam is so controlled that the FeO forms,above grid 5, a dense ebullient mass of solids fluidized by the upwardlyflowing steam and hydrogen generated to form a well defined upper level8 at a bed height of about -25 ft. and a pressure of about 100 lbs. persq. in. A superficial gas velocity of about 0.3-1 ft. per second withinreactor I0 is suitable for this purpose at the particle sizes abovespecified. The fluid solids bed in reactor l0 assumes a uniformtemperature of about 1100 F. at which rapid reduction of steam intohydrogen takes place.

Hydrogen of about 100 lbs. pressure containing unconverted steam passesoverhead from level 8 through a conventional gas-solids separator, suchpressure in standpipe l8 decreases from bottom to top so as to cause thedesired solids flow therethrough. The solids from pipe l8 may dischargeinto line 22 wherein they are picked up by air as cyclone l2 and throughline H to a conventional recovery and storage system (not shown) or toany desired use such as a synthesis reactor preferably after heatexchange with process fluids. Solids separated in cyclone l2 may bereturned through pipe l3 to the fluidized bed in reactor l0. Cyclone l2may also be arranged outside of reactor l0, if desired, downstream ofsuitable cooling means.

Finely divided oxidized solids of an average composition approachingF6304 are withdrawn downwardly under the pressure of reactor l0 throughline l6 and passed under said pressure upwardly through a reversestandpipe l8 provided with control valve 20 and communicating with lowpressure zone 30. Reverse standpipe I8 is supplied with small amounts ofa fluidizing gas such as air, methane or the like through one or moretaps l9. lit will be appreciated that the supplied from blower 24 at apressure of about 5 lbs. per sq. in. or they may pass on through pipeIlla and valve 200. directly into regenerator 30.

The solids-in-air suspension formed in line 22 is passed to the lowerconical portion of regener ator 30 which it enters through adistributing grid 26. A reducing and combustible gas such as methane issupplied to regenerator 30 via line 28. The amount of methane suppliedmust be sufficient to reduce the F830; present to FeO and, in addition,to consume all the available oxygen in a heat-generating combustionsupplying the heat required to maintain the desired reductiontemperature of about 1400" F, The linear gas velocities in regenerator30 are such as will establish a fluidized bed having a level 21 abovegrid 26 and contact times similar to those specified for reactor Ill.The pressure of regenerator 30 is preferably substantially atmospheric.

Spent reducing and flue gas leaves regenerator 30 through cyclone 32 andline 36 at substantially atmospheric pressure and the high temperatureof the regenerator, to be discarded or used for suitable purposes,preferably, after heat exchange with process fluids. Solids separated incyclone 32 may be returned to regenerator 30 through pipe 34. Cyclone 32may be arranged outside regenerator 30 as described in connection withcyclone l2.

Fluidized solids having an average composition approaching Feaos arewithdrawn downwardly from regenerator 30 through standpipe 45 providedwith steam aeration taps 42 and a control valve 44. standpipe 40 shouldhave a height of about ft. between grid 26 and valve 44 at the pressureconditions here involved, to force the fluidized Fe304 through valve 44under a pseudo-hydrostatic pressure of about lbs, per sq. in. into steamline I. The steam supplied through taps 42 is preferably preheated inheat exchange with spent gases from line 36 to avoid heat losses of themetal oxide on its path through standpipe 40.

When the solids circulation through standpi es l8 and 40 is maintainedat about 1 lb. of iron per SCF of H2 produced, no extraneous heat needbe supplied to reactor in in addition to the sensible heat of the FeaOrand the preheat of the steam.

The system illustrated permits of various modi fications in designandoperation. For example, instead of using a reverse standpipe l8, thesolids withdrawn from reactor Ill may be passed from line l6 directlyinto air line 22 or gas line 28 although this modification requirescompression of the gases supplied to lines 22 or 28. standpipe 50 may beprovided alternatively or in addition to standpipe 40 to permit solidscirculation from regenerator 30 to reactor in independent of the steamsupply. Countercurrent flow of solids and gases may be arranged ineither or both of zones Ill and 30 by establishing two or moresuperimposed fluidized beds, feeding the solids to the top bed and thegases to the lowermost bed while separating the beds by grids, such asgrid 26a, provided with overflows "a, as shown in regenerator 30, sothat one or more additional levels 2111 are formed. In this manner thesize of the treating vessel may be reduced as a result of the moreemcient utilization of the solid reactants.

The gaseous reducing agent and fuel supplied through line 28 may bereplaced or supplemented FeO and FeaO4 may be selected from thosementioned above. Further modifications within the scope of my inventionwill occur to those skilled in the art. 1

My invention will be further illustrated by the following specificexamples.

Example I For the production of 12 million standard cu. ft. of hydrogenper day suitable operating conditions in a system of the typeillustrated in the drawing are as follows:

System 3Feo+H2oz= Fe3o4+Hz Regenerator tempera- 'ture 1500 F.

Regenerator pressure 5 lbs./sq. in. gauge Reactor temperature; 1370 F,

Reactor pressure 100 lbs/sq. in. gauge Regenerator air 23.4 MM. SCF/DNatural gas to regenerator 6.85 MM. SCF/D Air+natural gas preheat 1300F. Steam to reactor 75,000 lbs/hr. Steam preheat 1000 F. Solidscirculation 350 tons/hr. Elevation of regenerator above reactor 100 ft.

Example II For the production of 12 million standard cu. ft. of hydrogenper day using a relatively undesirable hydrogen as the reducing agent inthe regenerator suitable operating conditions are as iollows:

System Fe+HzO2Fe0+Hz Regenerator temperature 1200 F. Regeneratorpressure 5lbs./sq. in. gauge Reactor temperature 1100 F. Reactorpressure 15 lbs/sq. in.gaug'e Regenerator air None Total impure Hz toregenerator MM. SCF/D Net fresh impure H2 13 MM. SCF/D Hz-preheat 1225F'. Steam to reactor 30,000 lbs./hr. Steam preheat 1125 F. Solidscirculation 160 tons/hr. Elevation of regenerator above reactor 15 ft.

The foregoing description and exemplary operations have served toillustrate specific applications and results of my invention. However,

other modifications obvious to those skilled in the art are within thescope of my invention. Only such limitations should be imposed on the.invention as are indicated in the appended claims.

I claim:

1. A continuous process for producing hydrogen by reacting steam withmetalliferous reducing agents which comprises contacting steam in ahydrogen generation zone at a steam reducing temperature and an elevatedpressure of between about 70 and 1500 lbs. per sq. in. gage with .adense, turbulent, ebullient mass of a finely divided solid metalliferousreducing agent fluidized by an upwardly flowing gas to form a welldefined upper level, recovering hydrogen overhead from said level,withdrawing fluidized spent solid agent downwardly from said mass,passing withdrawn spent agent under the pseudo-hydrostatic pressure of afluidized column of said spent agent upwardly to an elevatedregeneration zone, contacting said spent agent in said regeneration zonewith a fluid regenerating agent at a regenerating temperature and at apressure substantially lower than said elevated pressure, in the form ofa second dense, turbulent, ebullient mass of a finely. divided solidfluidized by an upwardly flowing gas to form a well defined upper level,withdrawing fluidized regenerated solid reducing agent downwardly fromsaid second mass, and passing withdrawn regenerated agent under thepseudo-hydrostatic pressure of a second fluidized column of saidregenerated agent to said generation zone, said second column having aheight not exceeding about 200 ft. and an apparent density of about to250 lbs. per cu. ft., and the diflerential between said elevated andlower pressures as determined by said height, amounting to about -300lbs. per sq. in.

2. The process of claim 1 wherein said metalliferous reducing agent ispredominantly FeO and said spent agent is predominantly F8304.

3. The process of claim 1 wherein said height is about ft. and saidpressure differential about 100 lbs. per sq. in.

FRANK T. BARR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 2,414,852 Burnside et al Jan. 28, 1947

